Actuator pivot shaft rolling bearing with seal

ABSTRACT

A variable turbine geometry turbocharger with an actuator pivot shaft with a rolling-element bearing having a rolling element between an inner race and outer race. Replacing a standard actuator shaft bushing with a rolling-element bearing may reduce friction and adverse movement in certain applications. Various seals may be feasible, such as a face seal attached to the inner or outer bearing race that could seal against the opposing race.

BACKGROUND

1. Field of the Disclosure

This disclosure relates to turbochargers with variable turbine geometrywith an actuator pivot shaft. Specifically, this disclosure relates toreplacing a standard actuator shaft bushing with a rolling-elementbearing.

2. Description of Related Art

Advantages of turbocharging include increased power output, lower fuelconsumption and reduced pollutant emissions. The turbocharging ofengines is no longer primarily seen from a high-power performanceperspective, but is rather viewed as a means of reducing fuelconsumption and environmental pollution on account of lower carbondioxide (CO₂) emissions. Currently, a primary reason for turbochargingis using exhaust gas energy to reduce fuel consumption and emissions. Inturbocharged engines, combustion air is pre-compressed before beingsupplied to the engine. The engine aspirates the same volume of air-fuelmixture as a naturally aspirated engine, but due to the higher pressure,thus higher density, more air and fuel mass is supplied into acombustion chamber in a controlled manner. Consequently, more fuel canbe burned, so that the engine's power output increases relative to thespeed and swept volume.

In exhaust gas turbocharging, some of the exhaust gas energy, whichwould normally be wasted, is used to drive a turbine. The turbineincludes a turbine wheel that is mounted on a shaft and is rotatablydriven by exhaust gas flow. The turbocharger returns some of thisnormally wasted exhaust gas energy back into the engine, contributing tothe engine's efficiency and saving fuel. A compressor, which is drivenby the turbine, draws in filtered ambient air, compresses it, and thensupplies it to the engine. The compressor includes a compressor impellerthat is mounted on the same shaft so that rotation of the turbine wheelcauses rotation of the compressor impeller.

Turbochargers typically include a turbine housing connected to theengine's exhaust manifold, a compressor housing connected to theengine's intake manifold, and a center bearing housing coupling theturbine and compressor housings together. The turbine housing defines avolute that surrounds the turbine wheel and that receives exhaust gasfrom the engine. The turbine wheel in the turbine housing is rotatablydriven by an inflow of exhaust gas supplied from the exhaust manifold.

A variable turbine geometry (VTG) turbocharger allows a turbine flowcross-section leading to the turbine wheel to be varied in accordancewith engine operating points. This allows the entire exhaust gas energyto be utilized and the turbine flow cross-section to be set optimallyfor each operating point. As a result, the efficiency of theturbocharger and hence that of the engine can be higher than thatachieved with bypass control of a wastegate valve assembly. Variableguide vanes in the turbine have an effect on pressure build-up behaviorand, therefore, on the turbocharger power output.

A VTG pivot shaft is typically not fitted directly to a bore in theturbine housing, but more often to a stationary bearing in a bore in theturbine housing. The pivot shaft is often radially located in a bearing,which can be located either in a bore, with a centerline within theturbine housing, or directly in the bearing housing depending on thedesign.

Borg Warner's US 2011/037639 for a “Control Shaft Seal” discloses amethod for keeping an “actuator pivot shaft” concentric in its bore toenhance the sealing capability thus maximizing the retention of theexhaust gases within the turbocharger and minimizing the escape ofexhaust gases to the environment external to the turbocharger.

Other VTG actuator pivot shafts can experience significant wear incertain applications during operation, presumably from high pressureloading between the bushing and shaft near the fork end of the shaft(turbine side). Lack of lubrication can cause high friction forcesbetween the shaft and bearing components, reducing available VTGactuation torque. Furthermore, in certain operations, it may bedifficult to seal the shaft to the bearing housing because of clearancebetween the shaft and bushing and the associated misalignment of theshaft to the bushing/housing.

This disclosure focuses on a rolling-element bearing for a VTG actuatorpivot shaft, and forces and movement between the shaft and bearingcomponents.

SUMMARY

An actuator pivot shaft bearing assembly may have a rolling-elementbearing with a rolling element between an outer race and an inner racewith a face seal, which can operate adjacent to the VTG lever. Arolling-element bearing can replace standard actuator shaft bushing.

The rolling-element bearing is a bearing that carries a load by placinground rolling elements between bearing rings/races. The relative motionof the pieces causes the round elements to roll with little rollingresistance and with little sliding.

The rolling-element bearing might reduce friction and could be designedfor minimal axial and radial movement. This could allow for varioustypes of seals, such as a face seal that is attached to the inner orouter bearing race and could seal against the opposing race. The axiallocation and surface finish between the two races could be tightlycontrolled.

BRIEF DESCRIPTION OF THE DRAWING

Advantages of the present disclosure will be readily appreciated as thesame becomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawingwherein FIG. 1 is a cross-sectional view of a turbocharger's actuatorpivot shaft bearing assembly with rolling-element bearing with a rollingelement between an outer race and an inner race with a face seal.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A turbocharger is generally known and includes a turbine and acompressor, wherein a compressor impeller is rotatably driven via arotating shaft by a turbine wheel. The rotating shaft passes through abearing housing between a turbine housing and a compressor housing.

The variable turbine geometry (VTG) turbocharger 10 may include anactuator pivot shaft assembly 12 as shown in FIG. 1 with a portionbetween a large block 14 and a VTG lever 16 with a ball 17 on the VTGlever 16. The actuator pivot shaft 18 defines an axis of rotationpartially surrounded by a rolling-element bearing 20.

The VTG turbocharger 10 may include an actuator pivot shaft bearingassembly 12 with a rolling-element bearing 20 with a rolling element 21between an inner race 22 and outer race 24. The inner race 22 is closestto the actuator pivot shaft 18 with a smaller circumference than theouter race 24. The rolling elements 21 used in rolling-element bearings20 is shown in the figure as a cylindrical roller, but balls, taperedrollers, spherical rollers, and needles are known rolling elements. Aparticularly common kind of rolling-element bearing 20 is the ballbearing, wherein the bearing has inner and outer races between whichballs roll. The rolling-element bearing 20 could be designed for minimalaxial and radial movement. The axial location and surface finish betweenthe two races 22 and 24 could be tightly controlled. Replacing astandard actuator shaft bushing with a rolling-element bearing 20 mayreduce friction and adverse movement.

Various seals may be feasible, such as a face seal 30 attached to theinner and/or outer race 22 and/or 24 that could seal against theopposing race 22 or 24.

The invention has been described in an illustrative manner, and it is tobe understood that replacing a standard actuator shaft bushing with arolling-element bearing 20 may not warrant patent protection, and thisdisclosure is a defensive publication replacing a standard actuatorshaft bushing with a rolling-element bearing 20. BorgWarner and theinventor waive any right to receive a patent on the disclosure of therolling-element bearing 20 replacing a standard actuator shaft bushing.

What is claimed is:
 1. A variable turbine geometry turbochargerincluding an actuator pivot shaft bearing assembly with arolling-element bearing with a cylindrical rolling element between aninner race and outer race and a face seal attached to the inner race andthat seals against the outer race.